Mo enzymes catalyze a number of two electron redox reactions in plants, animals and microorganisms, among which are NO3- and CO2 reduction, and purine and SO32- oxidation. These enzymes appear to have a role in xanthinuria, gout and uricemia and, possibly, artherosclerosis and coronary heart disease in humans, as well as Fe absorption and SO32- detoxification in mammals. Deficiency of sulfite oxidase produces neurological abnormalities, mental retardation and early death in children. The objective of the research is the elucidation of the structure and function of Mo enzymes by a study of model Mo complexes. This will be accomplished by the synthesis and characterization of Mo complexes which model the spectroscopic parameters, electrochemical behavior and reactivity with substrates of the enzymes. These complexes will be characterized by analysis, IR, electronic and NMR spectroscopy and their structures determine by x-ray crystallography. EPR parameters and electro-chemical reduction potentials will be determined. Redox reactions of these complexes with biologically relevant substrates will be investigated, kinetic parameters determined and reaction mechanisms proposed and tested. Results will be applied to the determination of the structue and function of the enzyme Mo centers.